When the drive wheel makes one revolution per minute, the unit of time may be the second. The drive mechanism can then form a deadbeat seconds mechanism, arranged to release the jumping element once per second. A deadbeat seconds mechanism comprises a deadbeat seconds indicator, generally a large hand at the centre of the dial, which “jumps” once per second. These mechanisms are extremely complicated to make. However they sometimes lack accuracy, as the “jumps” are made at ⅚ths of a second in some cases. They are also high energy consumers.
Some of these mechanisms are powered by a second energy source, specific to the deadbeat seconds mechanism, in addition to the main energy source required for the movement.
Other mechanisms are powered by the energy source of the movement, of the type described in the preamble. Such mechanisms are known to those skilled in the art and are described, for example, in CH Patent No 311865. In such mechanisms, the deadbeat seconds cam has a large number of teeth (30), involving small angular steps, which makes the jumps very sensitive to imperfections in the deadbeat seconds cam. Further, the same pallet-stone of the deadbeat seconds pallet-lever is used for cooperating both with the deadbeat seconds cam and the fourth wheel. The deadbeat seconds pallet-lever blocks the jumping element under the effect of force from the coupling spring and friction. This friction absorbs a relatively large amount of power, and therefore the energy consumed by the deadbeat seconds mechanism is high.